Abstract

Accreting supermassive black hole binaries are powerful multimessenger sources emitting both gravitational and electromagnetic (EM) radiation. Understanding the accretion dynamics of these systems and predicting their distinctive EM signals is crucial to informing and guiding upcoming efforts aimed at detecting gravitational waves produced by these binaries. To this end, accurate numerical modeling is required to describe both the spacetime and the magnetized gas around the black holes. In this work, we present two key advances in this field of research. First, we have developed a novel 3D general relativistic magnetohydrodynamics (GRMHD) framework that combines multiple numerical codes to simulate the inspiral and merger of supermassive black hole binaries starting from realistic initial data and running all the way through merger. Throughout the evolution, we adopt a simple but functional prescription to account for gas cooling through photon emission. Next, we have applied our new computational method to follow the time evolution of circular, equal-mass black hole binaries with different black hole spin configurations for ~200 orbits, starting from a separation of 20 gravitational radii and reaching the post-merger evolutionary stage of the system. We illustrate the spin-induced differences in the structure of the minidisks orbiting each black hole during the early inspiral. We show how mass continues to flow toward the binary even after the binary "decouples" from its surrounding disk, but the accretion rate onto the black holes diminishes. We identify how the minidisks are slowly drained and eventually dissolve as the binary compresses. We confirm previous findings that the system's luminosity decreases by a factor of a few during inspiral; however, we observe an abrupt increase by ~50--100% (depending on the binary's spin setup) in this quantity at the time of merger, likely accompanied by an equally abrupt change in spectrum. We demonstrate that during the inspiral, fluid ram pressure regulates the fraction of the magnetic flux transported to the binary that attaches to the black holes' horizons. Finally, we explore the spin-dependent dynamics of jet launching and jet-jet interaction and discuss the potentially associated electromagnetic signatures.

Library of Congress Subject Headings

Accretion (Astrophysics); Black holes (Astronomy); Double stars; Stars--Evolution

Publication Date

8-22-2025

Document Type

Dissertation

Student Type

Graduate

Degree Name

Astrophysical Sciences and Technology (Ph.D.)

Department, Program, or Center

Physics and Astronomy, School of

College

College of Science

Advisor

Manuela Campanelli

Advisor/Committee Member

Yosef Zlochower

Advisor/Committee Member

George Thurston

Campus

RIT – Main Campus

Plan Codes

ASTP-PHD

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